Radiation imaging apparatus

ABSTRACT

A radiation imaging apparatus includes a pixel array where a plurality of pixels configured to detect radiation are arrayed, a sensor configured to detect radiation irradiation for exposure control, a reader configured to read out signals from the plurality of pixels and the sensor, and a processor configured to process the signals read out by the reader. The processor corrects, based on the signals read out from the sensor by the reader, the signals read out from the plurality of pixels by the reader.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a radiation imaging apparatus.

Description of the Related Art

As a radiation imaging apparatus which captures an image of radiationsuch as X-rays, a radiation imaging apparatus with a radiation imagingpanel where conversion elements which convert radiation into charges arearrayed two-dimensionally is known. Some conversion elements convertradiation into visible light and then convert this visible light intothe charges, or convert radiation into the charges directly. Eachconversion element includes a semiconductor layer. A dark currentgenerated in this semiconductor layer becomes an offset component tocause shading.

Japanese Patent Laid-Open No. 2011-223088 has described an imagingapparatus which corrects, based on a dark signal amount by a darkcurrent, charge information at the time of radiation irradiation. Theimaging apparatus described in Japanese Patent Laid-Open No. 2011-223088includes a plurality of temperature sensors on the periphery of aconversion layer which converts information on light or radiation intocharge information and measures a temperature distribution by thesesensors. When capturing a radiation image, a dark signal amount isobtained based on the correlation between the temperature distributionand the dark signal amount stored in advance and the temperaturedistribution obtained by using the plurality of temperature sensors, andthe charge information is corrected based on this dark signal amount. Ina method described in Japanese Patent Laid-Open No. 2011-223088,correction is made based on the correlation between the temperaturedistribution and the dark signal amount stored in advance, and thetemperature distribution measured when capturing the radiation image.Therefore, the temperature sensors and a memory which stores thecorrelation are indispensable, complicating an arrangement. In themethod, a dark signal amount is not actually measured at the time ofimage capturing. As a result, a deviation may occur between the darksignal amount obtained based on the correlation and the actual darksignal amount.

A radiation imaging apparatus having an exposure control function isalso known. Japanese Patent Laid-Open No. 2012-247354 has described aradiation image detection apparatus which detects at least one of thestart and the end of radiation irradiation. The radiation imagedetection apparatus includes an imaging region where a plurality ofpixels are arrayed in a matrix and a plurality of detection elementswhich output electrical signals corresponding to the incident amount ofradiation. The radiation image detection apparatus detects at least oneof the start and the end of radiation irradiation based on the output ofa detection element having a high sensitivity out of the plurality ofdetection elements.

Note that a technique of correcting a radiation image based oninformation obtained by a detection element or sensor for exposurecontrol is not known.

SUMMARY OF THE INVENTION

One embodiment of the present invention provides a techniqueadvantageous in removing a noise component more accurately with a simplearrangement.

One embodiment of the present invention provides a radiation imagingapparatus comprising: a pixel array where a plurality of pixelsconfigured to detect radiation are arrayed; a sensor configured todetect radiation irradiation for exposure control; a reader configuredto read out signals from the plurality of pixels and the sensor; and aprocessor configured to process the signals read out by the reader,wherein the processor corrects, based on the signals read out from thesensor by the reader, the signals read out from the plurality of pixelsby the reader.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments with reference to theattached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the arrangement of a radiation imagingsystem according to an embodiment of the present invention;

FIG. 2 is a view showing the arrangement of a radiation imaging panelaccording to the first embodiment of the present invention;

FIG. 3 is a timing chart showing an operation example of the radiationimaging system according to an embodiment of the present invention;

FIG. 4 is a timing chart showing another operation example of theradiation imaging system according to an embodiment of the presentinvention;

FIG. 5 is a view showing the arrangement of a radiation imaging panelaccording to the second embodiment of the present invention; and

FIG. 6 is a view showing the arrangement of a radiation imaging panelaccording to the third embodiment of the present invention.

DESCRIPTION OF THE EMBODIMENTS

A radiation imaging system of the present invention will exemplarily bedescribed below through embodiments thereof with reference to theaccompanying drawings.

FIG. 1 shows the arrangement of a radiation imaging system 10 accordingto an embodiment of the present invention. The radiation imaging system10 can include, for example, a radiation imaging apparatus 100, acontroller 200, a radiation generator 310, and a radiation emissioncontroller 320. All or part of the arrangement of the controller 200 maybe integrated in the radiation imaging apparatus 100. An apparatusconstituted by all or part of the arrangement of the radiation imagingapparatus 100 and all or part of the arrangement of the controller 200can also be recognized as the radiation imaging apparatus. Thecontroller 200 and the radiation emission controller 320 may beimplemented as one apparatus.

The radiation imaging apparatus 100 can include, for example, a pixelarray 110, one or a plurality of sensors S, a driver 120, a reader 130,an amplifier (impedance converter) 140, a D/A converter 150, a processor160, a control unit 170, and a wireless interface (I/F) 180. A pluralityof pixels which detect radiation are arrayed in the pixel array 110. Theone or the plurality of sensors S are typically arranged in an imagingarea IA constituted by the plurality of pixels in the pixel array 110.Further, the plurality of sensors S can typically be arrayed in theimaging area IA in a distributed manner.

The driver 120 drives the plurality of pixels in the pixel array 110 andthe one or the plurality of sensors S. The reader 130 reads out signalsfrom the plurality of pixels in the pixel array 110 and the one or theplurality of sensors S. The signals read out from the sensors S by thereader 130 can be used for exposure control, correction of a radiationimage captured by the pixel array 110, or the like. The amplifier 140amplifies the signals read out by the reader 130. The D/A converter 150converts a signal (analog signal) output from the amplifier 140 into adigital signal.

The processor 160 processes signals read out by the reader 130 from theplurality of pixels which constitute the pixel array 110 and signalsread out by the reader 130 from the one or the plurality of sensors S.For example, the processor 160 corrects, based on the signals read outby the reader 130 from the one or the plurality of sensors S, thesignals read out by the reader 130 from the plurality of pixels whichconstitute the pixel array 110. In this embodiment, the signalsprocessed by the processor 160 are signals obtained by processing thesignals output from the reader 130 with the amplifier 140 and the D/Aconverter 150. However, the processor 160 may be configured to processthe signals supplied from the reader 130 without passing through theamplifier 140 and/or the D/A converter 150 because the signals outputfrom the reader 130, the amplifier 140, and the D/A converter 150 areequal to each other.

The processor 160 generates an exposure control signal based on thesignals read out by the reader 130 from the one or the plurality ofsensors S in a state in which the radiation imaging apparatus 100 isirradiated with radiation. The exposure control signal can be obtainedby correcting, based on the signals read out by the reader 130 from theone or the plurality of sensors S in a radiation non-irradiation state,the signals read out by the reader 130 from the one or the plurality ofsensors S in a radiation irradiation state.

The control unit 170 controls the pixel array 110, the one or theplurality of sensors S, the driver 120, the reader 130, the amplifier140, the D/A converter 150, the processor 160, and the wireless I/F 180.Further, based on the exposure control signal generated by the processor160, the control unit 170 sends a radiation emission stop command to theradiation emission controller 320 via the controller 200 so as to stopradiation irradiation by the radiation generator 310.

The wireless I/F 180 communicates with the controller 200 (a wirelessI/F 220 thereof). The wireless I/F 180 transmits, to the controller 200,the signal supplied from the processor 160, the radiation emission stopcommand, a signal indicating the state of the radiation imagingapparatus 100, and the like. The wireless I/F 180 receives, from thecontroller 200, information indicating that the radiation emissioncontroller 320 has transmitted a radiation emission command to theradiation generator 310 (to be referred to as radiation emissionnotification information) or the like.

The controller 200 can include, for example, a processor 210, a wirelessI/F 220, a display unit 230, and an input unit 240 (a keyboard, apointing device, or the like). The controller 200 can be formed byintegrating software (computer program) in a general-purpose computer.

The radiation emission controller 320 includes a radiation emissionswitch (not shown). The radiation emission controller 320 transmits theradiation emission command to the radiation generator 310 in response toturning on of the radiation emission switch and notifies the radiationemission controller 320 of this. The radiation generator 310 emitsradiation in accordance with the radiation emission command. Thecontroller 200 transmits, to the radiation imaging apparatus 100,radiation emission notification information indicating that theradiation emission command is transmitted to the radiation generatorfrom the radiation emission controller 320.

FIG. 2 shows the arrangement of the radiation imaging apparatus 100according to the first embodiment of the present invention. A pluralityof pixels P are arrayed two-dimensionally in the pixel array 110 so asto form a plurality of rows and a plurality of columns. The imaging areaIA is formed by arraying the plurality of pixels P. The plurality ofsensors S can be arrayed in a distributed manner in the imaging area IA.In an example shown in FIG. 2, the plurality of sensors S are arrayed ona diagonal line of the imaging area IA. However, this is merely aschematic view and, in practice, the plurality of sensors S can bearranged to be assigned for each group constituted by the plurality ofpixels P. In the example shown in FIG. 2, the pixels P are not arrangedat coordinates (positions specified by the rows and the columns in thearray of the pixels P) where the sensors S are arranged. However, thesensors S smaller than the pixels P arranged at other coordinates may bearranged at the coordinates.

Each pixel P includes a conversion element CV and a switch TT.Similarly, each sensor S also includes the conversion element CV and theswitch TT. Each conversion element CV converts radiation into charges.Each conversion element CV can be constituted by a scintillator whichconverts radiation into visible light and a photoelectric conversionelement which converts visible light into the charges. In this case, theplurality of conversion elements CV can share the scintillator. Eachconversion element CV may be configured to directly convert radiationinto the charges. Each conversion element CV can be constituted by a MISor a PIN photoelectric conversion element. Each switch TT can beconstituted by, for example, a thin-film transistor (TFT). Each switchTT is arranged between one electrode of the conversion element CV and asignal line SL so as to control the connection between them. The otherelectrode of each conversion element CV is connected to a bias line Bs.

The driver 120 includes a pixel driver 121 which drives the plurality ofpixels P and a sensor driver 122 which drives the one or the pluralityof sensors S. The gate of the switch TT in each pixel P is connected toone of gate lines G1 to Gm driven by the pixel driver 121. Note that thegate lines G1 to Gm drive the pixels P of the first row to the mth row.The gate of the switch TT in each sensor S is connected to one of gatelines G1′ to Gm′ driven by the sensor driver 122. Note that the gatelines G1′ to Gm′ drive the sensors S of the first row to the mth row.

The reader 130 reads out a signal from each pixel P or each sensor S viathe signal line SL. The reader 130 includes, for each column in thepixel array 110, an integrating amplifier (amplifier) 131, a variableamplifier 132, a sample and hold circuit 133, and a buffer amplifier134. The signal output to each signal line SL is amplified by theintegrating amplifier 131 and the variable amplifier 132, sampled andheld by the sample and hold circuit 133, and amplified by the bufferamplifier 134. The reader 130 includes a multiplexer 135. The signaloutput from the buffer amplifier 134 provided for each column isselected by the multiplexer 135 and output to the amplifier 140.

Each integrating amplifier 131 includes an operational amplifier, anintegral capacitor, and a reset switch. The signal output to each signalline SL is input to the inverting input terminal of an operationalamplifier 105, a reference voltage Vref is input to the non-invertinginput terminal, and the amplified signal is output from the outputterminal. The integral capacitor is arranged between the inverting inputterminal and the output terminal of the operational amplifier. Eachvariable amplifier 132 amplifies the signal from the integratingamplifier 131 at an amplification factor designated by the control unit170. Each sample and hold circuit 133 can be formed from a samplingswitch and a sampling capacitor.

The operation of the radiation imaging system 10 will exemplarily bedescribed with reference to FIG. 3. In FIG. 3, a “radiation emissioncommand” is transmitted from the radiation emission controller 320 tothe radiation generator 310 and commands a change from low level to highlevel. “Radiation” is generated by the radiation generator 310,indicates that radiation is emitted at high level, and indicates thatradiation is not emitted at low level. A “state” indicates the state ofeach pixel P in the pixel array 110. Each of “VG1′” to “VGm′” indicatesthe logical level of each of the gate lines G1′ to Gm′ driven by thesensor driver 122. Each of “VG1” to “VGm” indicates the logical level ofeach of the gate lines G1 to Gm driven by the pixel driver 121. A“signal from a DAC” is output from the reader 130 via the amplifier 140and the D/A converter 150.

In a period (t1 to t2) until the radiation emission notificationinformation is received from the controller 200, the control unit 170controls the sensor driver 122 to sequentially drive the gate lines VG1′to VGm′ to an active level. When each of the gate lines VG1′ to VGm′becomes the active level, the switch TT having the gate connected to itis turned on and the sensor S (the conversion element CV thereof) havingthe switch TT is reset. Note that resetting each sensor S means removingthe charges accumulated in the conversion element CV of each sensor S.That is, the sensors S are reset periodically until the radiationemission notification information is received from the controller 200.

Similarly, in the period (t1 to t2) until the radiation emissionnotification information is received from the controller 200, thecontrol unit 170 controls the pixel driver 121 to sequentially drive thegate lines VG1 to VGm to the active level. When each of the gate linesVG1 to VGm becomes the active level, the switch TT having the gateconnected to it is turned on and the pixel P (the conversion element CVthereof) having the switch TT is reset. Note that resetting each pixel Pmeans removing the charges accumulated in the conversion element CV ofeach pixel P. That is, the pixels P are reset periodically until theradiation emission notification information is received from thecontroller 200.

Typically, the number of rows where the sensors S are arranged issmaller than the number of rows of the pixels P which constitute thepixel array 110. Further, a period during which the active-level signalis applied to the gate of the switch TT in each sensor S can be setshorter than a period during which the active-level signal is applied tothe gate of the switch TT in each pixel P. Furthermore, a time requiredto reset all the sensors S (one cycle for resetting) can be set shorterthan a time required to reset all the pixels P (one cycle forresetting).

In response to reception (t2) of the radiation emission notificationinformation from the controller 200, the control unit 170 stopsperiodical resetting the pixels P of the pixel array 110. Note thatperiodical resetting of the pixels P in the pixel array 110 ispreferably stopped by the time radiation irradiation from the radiationgenerator 310 is started after the reception (t2) of the radiationemission notification information from the controller 200. A timeelapsed before radiation irradiation from the radiation generator 310 isstarted after the reception (t2) of the radiation emission notificationinformation from the controller 200 can be determined by, for example,the characteristics of the radiation generator 310 or the transmissiontime of the radiation emission notification information in the radiationemission controller 320 and the controller 200. Upon stopping periodicalresetting of the pixels P in the pixel array 110, accumulation of thecharges corresponding to radiation which irradiates the conversionelements CV is started in the pixels P of the pixel array 110.

Upon receiving the radiation emission notification information from thecontroller 200, in a first period (t2 to t3) determined by using thereception as a trigger, the control unit 170 controls the sensor driver122 and the reader 130 to read out offset signals from the plurality ofsensors S. The first period (t2 to t3) is started in response to thetransmission of the radiation emission command from the radiationemission controller 320 to the radiation generator 310. In the firstperiod (t2 to t3), noise is sampled, and radiation has not been emittedfrom the radiation generator 310 yet even though the radiation emissioncommand had been transmitted.

In the first period (t2 to t3), the control unit 170 controls the sensordriver 122 and the reader 130 to read out first noise from the pluralityof sensors S. The first noise can include, for example, offset noise ofthe reader 130, the amplifier 140, and the D/A converter 150, inaddition to dark current noise corresponding to the charges accumulatedin the sensors S owing to a dark current or the like after resetting thesensors S. The sensor driver 122 sequentially drives the gate lines VG1′to VGm′ to the active level in the first period. Assume that thecoordinates (positions) in the pixel array 110 is specified by thenumbers of the rows and columns formed by the pixels P. The first noiseread out from the sensor S arranged on the xth row and the yth column ofthe pixel array 110 is notated as n1(x, y). The first noise n1(x, y) isheld by a memory in the processor 160.

A later period (t3 to t4) includes a period during which the radiationimaging apparatus 100 is irradiated with radiation. In the period (t3 tot4), the control unit 170 controls the sensor driver 122 and the reader130 to periodically read out the signals from the plurality of sensors Sunder radiation irradiation. Further, the control unit 170 generates anexposure control signal based on the signals read out from the sensors Sby the reader 130 and detects, based on the exposure control signal,that radiation irradiation from the radiation generator 310 should beterminated. At this time, the control unit 170 generates, as an exposurecontrol signal, the difference between the signals read out from thesensors S by the reader 130 in the radiation irradiation state and thefirst noise n1(x, y) held in the first period in a radiation irradiationstate. Then, the control unit 170 detects, based on the exposure controlsignal, or more specifically, based on the integrated value of theexposure control signal, that radiation irradiation should be stopped.

When the integrated value reaches a predetermined value (t4), thecontrol unit 170 transmits, in response to this, the radiation emissionstop command to the radiation emission controller 320 via the controller200. In response to this, the radiation emission controller 320 causesthe radiation generator 310 to stop emitting radiation.

In a later period (t4 to t5), the control unit 170 controls the sensordriver 122 to sequentially drive the gate lines VG1′ to VGm′ to theactive level and resets the sensors S.

In a later second period (t5 to t6), the control unit 170 controls thesensor driver 122 and the reader 130 to read out, from the plurality ofsensors S, second noise n2(x, y) including a residual image componentai(x, y). The residual image component ai(x, y) is a signal generated asa result of an increase in the dark current by irradiating the sensors Swith radiation in the period (t3 to t4) and still remains afterresetting the sensors S.

The second noise n2(x, y) includes a noise component nearly equal to thefirst noise n1(x, y) and the residual image component ai(x, y). It istherefore possible to obtain the residual image component ai(x, y) bycalculating the difference between the second noise n2(x, y) and thefirst noise n1(x, y) (that is, n2(x, y)−n1(x, y)). The processor 160decides, based on the residual image component ai(x, y) obtained basedon the signals read out from the plurality of sensors S, residual imagecomponents ai′(x, y) at all coordinates (x, y) by interpolation or thelike. As will be described later, the residual image components ai′(x,y) are used to correct radiation image signals.

The residual image components become larger as the intensity ofradiation entering the radiation imaging apparatus 100 increases. Forexample, in the imaging area IA, the residual image component generatedin a portion where radiation enters without passing through an object islarger than the residual image component generated in a portion whereradiation which has passed through the object enters. The transmittanceof radiation varies depending on the tissue of the object. Therefore,the residual image components appear as information having densities inthe imaging area IA. The residual image components are included in thesignals read out from the pixels P irradiated with radiation, inaddition to the signals read out from the sensors S irradiated withradiation. The residual image components included in the signals readout from the pixels P are also signals generated as a result of theincrease in the dark current by irradiating the pixels P with radiationin the period (t3 to t4) and still remain after resetting the pixels P.In this embodiment, the residual image components included in thesignals read out from the pixels P irradiated with radiation are removedor reduced based on the residual image components ai′(x, y) obtainedbased on the signals read out from the sensors S.

In a period (t6 to t7), the control unit 170 controls the pixel driver121 and the reader 130 to read out the radiation image signals from theplurality of pixels P which constitute the pixel array 110. Let S(x, y)be the radiation image signals of the pixels P arranged at thecoordinates (x, y) read out by the reader 130 in the period (t6 to t7).The radiation image signals S(x, y) include a true radiation imagesignal I(x, y) and a noise image signal N(x, y). That is, S (x, y)=I (x,y)+N (x, y) holds.

In a later period (t7 to t8), the control unit 170 controls the pixeldriver 121 and the reader 130 to reset the plurality of pixels P whichconstitute the pixel array 110.

In a later period (t9 to t10), the control unit 170 controls the pixeldriver 121 and the reader 130 to read out noise image signals N′(x, y)from the plurality of pixels P which constitute the pixel array 110.Each noise image signal N′(x, y) includes noise nearly equal to thenoise image signal N(x, y) included in a radiation image signal A(x, y)and a residual image component AI(x, y). That is, N′(x, y)=N(x, y)+AI(x,y) holds.

Since the pixels P and the sensors S arranged in the positions close toeach other are irradiated with radiation nearly equally, the residualimage component AI(x, y) is strongly correlated to the residual imagecomponent ai(x, y). Therefore, for example, AI(x, y)=α×ai(x, y) holds.Note that α is a coefficient depending on, for example, time and thetiming of resetting in the pixels P and the sensors S, and can beobtained by a simulation, measurement, or the like.

By summarizing the above, the following equations hold.S(x,y)=I(x,y)+N(x,y)N′(x,y)=N(x,y)+AI(x,y)AI(x,y)=α×ai(x,y)These equations yield:

$\begin{matrix}\begin{matrix}{{I\left( {x,y} \right)} = {{S\left( {x,y} \right)} - {N\left( {x,y} \right)}}} \\{= {{S\left( {x,y} \right)} - \left( {{N^{\prime}\left( {x,y} \right)} - {{AI}\left( {x,y} \right)}} \right)}} \\{= {{S\left( {x,y} \right)} - {N^{\prime}\left( {x,y} \right)} + {\alpha \times {{ai}\left( {x,y} \right)}}}}\end{matrix} & (1)\end{matrix}$

That is, the processor 160 can obtain, based on equation (1), theradiation image signal I(x, y) with noise including the residual imagecomponents being removed or reduced. The radiation image signal I(x, y)obtained by the processor 160 can be sent to the controller 200 via thewireless I/F 180.

In an operation example shown in FIG. 3, the second noise n2(x, y) isread out before reading out the radiation image signals S(x, y) in theperiod (t6 to t7). However, this is merely an example. As shown in anoperation example shown in FIG. 4, the second noise n2(x, y) may be readout in the third period (t6 to t7) after reading out the radiation imagesignals S(x, y) in the period (t5 to t6). In reading out the radiationimage signals S(x, y), the pixel array 110, the driver 120, the reader130, the amplifier 140, the D/A converter 150, and the like consumeconsiderable power. The residual image components can be large owing toheat generated by the considerable power consumption. Therefore, it maybe more advantageous in reading, as in the operation example shown inFIG. 4, the second noise n2(x, y) after reading out the radiation imagesignals S(x, y) in order to detect the residual image components moreaccurately.

The above-described embodiment is merely an exemplary embodiment of thepresent invention, and various modifications can be made. For example,the first noise n1(x, y) may be obtained by using the sensors S in theperiod (t1 to t2). In this case, the reader 130 may read out the signalsfrom the sensors S instead of resetting the sensors S in the period (t1to t2).

In a reset operation, the switches of the pixels on odd numbered rowsmay be sequentially rendered conductive after sequentially rendering theswitches of the pixels on even numbered rows conductive. In a readoutoperation, the switches of the pixels from head rows to last rows may besequentially rendered conductive. Alternatively, the switches of thepixels from the head rows to the last rows may be sequentially renderedconductive in the reset operation, and the switches of the pixels on theodd numbered rows may be sequentially rendered conductive aftersequentially rendering the switches of the pixels on the even numberedrows conductive. Furthermore, in both of the reset operation and thereadout operation, the switches of the pixels on the odd numbered rowsmay be sequentially rendered conductive after sequentially rendering theswitches of the pixels on the even numbered rows conductive.

In the reset operation, not only the switches of the pixels on one roware rendered conductive at once, but the switches of the pixels on theplurality of rows may be rendered conductive at the same time. Forexample, the pixels on all the odd numbered rows may be reset whilerendering the pixels on the plurality of odd numbered rows conductive atthe same time after resetting the pixels on all the even numbered rowswhile rendering the pixels on the plurality of even numbered rowsconductive at the same time. The reset operation need not be performedin ascending order or descending order of the row numbers. The rowsreset continuously may not be adjacent to each other.

FIG. 5 shows the arrangement of a radiation imaging apparatus 100according to the second embodiment of the present invention. Mattersthat are not mentioned in the second embodiment can comply with thefirst embodiment. In the second embodiment, a reader 130 includes, asdedicated circuits configured to read out signals from sensors S, anintegrating amplifier (amplifier) 131′, a variable amplifier 132′, asample and hold circuit 133′, and a buffer amplifier 134′. Theintegrating amplifier 131′, the variable amplifier 132′, the sample andhold circuit 133′, and the buffer amplifier 134′ can have the samearrangements as those of integrating amplifiers (amplifiers) 131,variable amplifiers 132, sample and hold circuits 133, and bufferamplifiers 134, respectively.

FIG. 6 shows the arrangement of a radiation imaging apparatus 100according to the third embodiment of the present invention. Matters thatare not mentioned in the third embodiment can comply with the firstembodiment. In the third embodiment, a pixel array 110 includes aplurality of pixel rows and a plurality of sensor rows. Each pixel rowis constituted by a plurality of pixels P and each sensor row isconstituted by a plurality of sensors S. In FIG. 6, a row driven by agate line G2 is illustrated as the sensor row for the descriptiveconvenience. For example, the sensor rows can be provided at one to apredetermined number of pixel rows.

Other Embodiments

Embodiment(s) of the present invention can also be realized by acomputer of a system or apparatus that reads out and executes computerexecutable instructions (e.g., one or more programs) recorded on astorage medium (which may also be referred to more fully as a‘non-transitory computer-readable storage medium’) to perform thefunctions of one or more of the above-described embodiment(s) and/orthat includes one or more circuits (e.g., application specificintegrated circuit (ASIC)) for performing the functions of one or moreof the above-described embodiment(s), and by a method performed by thecomputer of the system or apparatus by, for example, reading out andexecuting the computer executable instructions from the storage mediumto perform the functions of one or more of the above-describedembodiment(s) and/or controlling the one or more circuits to perform thefunctions of one or more of the above-described embodiment(s). Thecomputer may comprise one or more processors (e.g., central processingunit (CPU), micro processing unit (MPU)) and may include a network ofseparate computers or separate processors to read out and execute thecomputer executable instructions. The computer executable instructionsmay be provided to the computer, for example, from a network or thestorage medium. The storage medium may include, for example, one or moreof a hard disk, a random-access memory (RAM), a read only memory (ROM),a storage of distributed computing systems, an optical disk (such as acompact disc (CD), digital versatile disc (DVD), or Blu-ray Disc (BD)™),a flash memory device, a memory card, and the like.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2014-194298, filed Sep. 24, 2014, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A radiation imaging apparatus comprising: a pixelarray where a plurality of pixels configured to detect radiation toobtain a radiation image are arrayed; a sensor configured to detectradiation irradiation; a reader configured to read out radiation imagesignals from the plurality of pixels and to read out sensor signals fromthe sensor; and a processor configured to process the radiation imagesignals and the sensor signals read out by the reader, wherein thesensor is reset after the radiation irradiation stops, the reader readsout the radiation image signals from the plurality of pixels after theradiation irradiation stops, reads out a first sensor signal from thesensor in a first period before the radiation irradiation starts, andreads out a second sensor signal from the sensor in a second periodafter the radiation irradiation stops and the sensor is reset, andbefore the radiation image signals are read out, and the processorcorrects the radiation image signals based on a difference between thefirst sensor signal and the second sensor signal.
 2. The apparatusaccording to claim 1, wherein the processor generates an exposurecontrol signal based on sensor signals read out from the sensor by thereader in a radiation irradiation state, and radiation irradiation by aradiation generator is stopped based on the exposure control signal. 3.The apparatus according to claim 2, wherein the processor corrects thesensor signals read out from the sensor by the reader in the radiationirradiation state, thereby generating the exposure control signal, basedon sensor signals read out from the sensor by the reader in a radiationnon-irradiation state.
 4. The apparatus according to claim 1, whereinthe difference includes a residual image component which is generated byirradiating the sensor with radiation and remains after resetting thesensor.
 5. The apparatus according to claim 1, wherein the reader readsout noise image signals from the plurality of pixels after reading outthe radiation image signals, and the processor corrects the radiationimage signals based on the noise image signals and the difference. 6.The apparatus according to claim 5, wherein the plurality of pixels arereset between readout of the radiation image signal and readout of thenoise image signal.
 7. The apparatus according to claim 6, wherein thesecond period is a period after the radiation irradiation stops, thesensor is reset, and the radiation image signals are read out, andbefore the noise image signal is read out.
 8. The apparatus according toclaim 1, wherein the first period is a period started in response toreceiving information indicating that a radiation emission command hasbeen transmitted to the radiation generator.
 9. The apparatus accordingto claim 1, wherein the sensor is arranged in an imaging areaconstituted by the plurality of pixels.
 10. A radiation imagingapparatus comprising: a pixel array where a plurality of pixelsconfigured to detect radiation to obtain a radiation image are arrayed;a sensor configured to detect radiation irradiation; a reader configuredto read out radiation image signals from the plurality of pixels and toread out sensor signals from the sensor; and a processor configured toprocess the radiation image signals and the sensor signals read out bythe reader, wherein the sensor is reset after the radiation irradiationstops, the reader reads out the radiation image signals from theplurality of pixels after the radiation irradiation stops, reads out afirst sensor signal from the sensor in a first period before theradiation irradiation starts, and reads out a second sensor signal fromthe sensor in a second period after the radiation irradiation stops andthe sensor is reset, and before the radiation image signals are readout, and the processor corrects, based on a difference between the firstsensor signal and the second sensor signal, the radiation image signalsso that a residual image component included in the radiation imagesignals is removed or reduced.
 11. The apparatus according to claim 10,wherein the processor generates an exposure control signal based onsensor signals read out from the sensor by the reader in a radiationirradiation state, and radiation irradiation by a radiation generator isstopped based on the exposure control signal.
 12. The apparatusaccording to claim 11, wherein the processor corrects the sensor signalsread out from the sensor by the reader in the radiation irradiationstate, thereby generating the exposure control signal, based on sensorsignals read out from the sensor by the reader in a radiationnon-irradiation state.
 13. The apparatus according to claim 10, whereinthe reader reads out noise image signals from the plurality of pixelsafter reading out the radiation image signals, and the processorcorrects the radiation image signals based on the noise image signalsand the difference.
 14. The apparatus according to claim 13, wherein theplurality of pixels are reset between readout of the radiation imagesignal and readout of the noise image signal.
 15. The apparatusaccording to claim 14, wherein the second period is a period after theradiation irradiation stops, the sensor is reset, and reading out theradiation image signals are read out, and before the noise image signalis read out.
 16. The apparatus according to claim 13, wherein the firstperiod is a period started in response to receiving informationindicating that a radiation emission command has been transmitted to theradiation generator.
 17. The apparatus according to claim 10, whereinthe sensor is arranged in an imaging area constituted by the pluralityof pixels.